1. Field of the Invention
The present invention relates to an endoscope system, a processor device, and a method for operating an endoscope system, for visualizing information related to an oxygen saturation level of hemoglobin in blood as an oxygen saturation image.
2. Description Related to the Prior Art
Recently, endoscope systems comprising a light source device, an endoscope device, and a processor device have been widely used in medical care. In addition to normal light observation using broadband white light as illumination light, blood-vessel-enhanced observation has come into practice. In the blood-vessel-enhanced observation, narrowband light with narrowband wavelengths is used to enhance blood vessels in an observation area in a display.
Furthermore, absorption properties of a blood vessel and light scattering properties of living tissue are used to extract biological functional information related to a blood vessel from an image signal obtained from the endoscope device. The biological functional information related to a blood vessel includes an oxygen saturation level of hemoglobin in blood and a depth of the blood vessel. The extracted biological functional information is visualized. For example, in Japanese Patent No. 2648494, different colors are assigned according to the oxygen saturation levels. A pseudo color oxygen saturation image is produced based on the assigned colors. The use of such oxygen saturation image facilitates finding a cancer which causes the oxygen saturation level exceptionally low, for example. Thereby diagnostic performance improves.
Generally, reflectivity of light in living tissue varies depending on three factors: an oxygen saturation level of hemoglobin in blood, a depth of a blood vessel, and a blood volume (which corresponds to the size of the blood vessel or density of the blood vessels). Although the Japanese Patent No. 2648494 is capable of visualizing distribution of the oxygen saturation levels as an image and displaying the image, influences of the depth of the blood vessel and a change in the blood volume on the oxygen saturation level are not considered. Hence, a less reliable image in which the oxygen saturation level of hemoglobin in blood is inaccurately visualized may be displayed in the case of the Japanese Patent No. 2648494.